The seven islands are mentioned in the Siddhānta-śiromaṇi:

bhūmer ardhaṁ kṣīra-sindhor udaka-sthaṁ
jambu-dvīpaṁ prāhur ācārya-varyāḥ
ardhe 'nyasmin dvīpa-ṣaṭkasya yāmye
kṣāra-kṣīrādy-ambudhīnāṁ niveśaḥ

śākaṁ tataḥ śālmala-matra kauśaṁ
krauñcaṁ ca go-medaka-puṣkare ca
dvayor dvayor antaram ekam ekaṁ
samudrayor dvīpam udāharanti

The seven islands (dvīpas) are known as (1) Jambu, (2) Śāka, (3) Śālmalī, (4) Kuśa, (5) Krauñca, (6) Gomeda, or Plakṣa, and (7) Puṣkara. The planets are called dvīpa. Outer space is like an ocean of air. just as there are islands in the watery ocean, these planets in the ocean of space are called dvīpas, or islands in outer space. There are nine khaṇḍas, known as (1) Bhārata, (2) Kinnara, (3) Hari, (4) Kuru, (5) Hiraṇmaya, (6) Ramyaka, (7) Ilāvṛta, (8) Bhadrāśva and (9) Ketumāla. These are different parts of the Jambūdvīpa. A valley between two mountains is called a khaṇḍa or varṣa.